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This paper focuses on studying the correlations of the performance of hard rock tunnel boring machines (TBMs) with operational and rock conditions. Firstly, a rigid-flexible coupled multibody dynamic model of an opening hard rock TBM is established for the analysis of its vibration. Then four performance indexes including mean vibration energy dissipation rate, dynamic specific energy (DSE), disc cutter wear rate, and load sharing coefficient are introduced and formulated, respectively, for evaluating the vibration level, excavation energy efficiency, cutter’s vulnerability to wear, and load transmission performance of cutterhead driving system of the TBM. Finally, numerical simulation results of the TBM tunneling performance evaluation are obtained and validated by on-site vibration measurement and tunneling data collection. It is found that operational and rock conditions exert important impact on TBM vibration level, excavation energy efficiency, and structure damage. When the type of rock to be cut changes from soft to hard with operational parameters held constant, TBM performance evaluated by these three indexes deteriorates significantly, and both the decrease of excavation energy efficiency and the increase of cutter wear rate caused by TBM vibration are obvious. This study provides the foundation for a more comprehensive evaluation of TBM performance in actual tunneling process.

With excellent capacity to cut rock up to 300 MPa, hard rock tunnel boring machines (TBMs) have been widely used in today’s tunnel excavation [

On the issue of TBM vibration, the dynamic characteristics of the cutterhead driving system with a joint cutterhead panel were investigated based on a multi-degree of freedom (MDOF) model [

Specific energy (SE), defined by energy consumed in cutting a unit volume of rock, has been widely applied to the performance evaluation of the rock cutting by disc cutter. The variation of SE was predicted for TBM operation in a hard and brittle crystalline rock of moderate strength with cutting tests [

The expenditure on disc cutter is at least one-fifth of the project cost and the time spent on replacing the cutter constitutes is about one-third of the total project time, which means that cutter failure is one of the major topics in TBM tunneling [

The load transmission performance of multiple pinions-gear ring meshing was evaluated for TBM’s cutterhead driving system by load sharing index considering meshing frequency, bearing stiffness, and mounting locations of pinions [

This paper presents a study of TBM performance evaluation considering operational and rock conditions from the aspects of vibration level, energy efficiency, cutter wear, and load transmission performance of cutterhead driving system. Following a statement of the problem to be investigated, a rigid-flexible coupled multibody dynamic model of an opening hard rock TBM is established for the vibration analysis of TBM. To deal with the performance evaluation problem, four indexes, namely, mean vibration energy dissipation rate, dynamic specific energy (DSE), disc cutter wear rate, and load sharing coefficient, are then introduced and formulated, respectively. Finally, numerical simulations are performed to obtain the results of the TBM performance varying with operational and rock conditions. The obtained numerical results are further validated through comparing with those from on-site vibration measurement and collected tunneling data.

An opening hard rock TBM consists essentially of a cutterhead driving system and a hydraulic thrust system, as shown in Figure

Schematics of an opening hard rock TBM.

Dynamic model of an opening hard rock TBM.

In Figure

The generalized displacement (i.e., the generalized DOFs) vectors of substructures are written as

TBM-rock interactions including disc cutter-rock interaction and bottom shield-rock mass nonlinear contact are mainly responsible for the vibration of TBM. These interactions correlate with a number of factors such as geotechnical parameters, cutter geometry, indentation, cutterhead rotation speed, and distribution of cutters on cutterhead [_{2}.

Generalized illustration of cutter-rock interaction.

The bottom shield-rock mass contact is considered in the dynamic modeling of the TBM. Shield slides on rock mass along tunneling direction when bottom shield-rock mass is in frictional contact, but this state transits to stick when the velocity vanishes due to vibration, and vice versa. Even in more serious vibration, bottom shield-rock mass contact separates, thus introducing discontinuities in TBM dynamic model. Rock mass serves as a support and can be modeled as a Winkler foundation, with damping springs uniformly distributed in both normal direction and tangential direction of shield circumference [

The equivalent normal and tangential distributed stiffness of Winkler foundation can be obtained by [

Mean vibration energy dissipation rate

Specific energy (SE) is the energy consumed in cutting a unit volume of rock and has been widely used to evaluate the cutting energy efficiency of a TBM disc cutter. The calculation of the current SE using mean cutting force eliminates the consideration of influence of vibration [

Disc cutter wear is the major one among cutter failure modes, which is determined by the amount of cutter wear. To estimate cutter’s vulnerability to wear, disc cutter wear rate is used. Based on CSM model shown in (^{−1} to 10^{−6},

The rotation of cutterhead of TBM is driven by multiple pinions-gear ring meshing. Small difference between meshing forces

The opening hard rock TBM used in an actual water tunnel project was taken as the application example in the evaluation of TBM performance. Structural parameters of the dynamic model of the opening hard rock TBM in numerical simulation are presented in Table ^{−6} and other parameters default. The rock conditions encountered in tunneling are complicated in terms of rock property. For simplicity but not loss of generality, three types of rock, namely, soft, moderately hard, and hard rock, respectively, are considered in numerical simulation. The average values of the relevant property of the three types of rock are listed in Table

Structural parameters in TBM dynamic model.

Structural parameters | |
---|---|

Mass of TBM (t) | 135 |

Diameter of cutterhead (m) | 4 |

Length of main machine (m) | 10 |

Number of pinions | 8 |

Number of cutters | 24 |

Cutter spacing (mm) | 84 |

Diameter of cutter (mm) | 432 |

Cutter tip width (mm) | 9.2 |

Parameters of three types of rock.

Rock type | Soft rock | Moderately hard rock | Hard rock |
---|---|---|---|

Young’s modulus (GPa) | 18 | 50 | 80 |

UCS (MPa) | 60 | 100 | 150 |

BTS (MPa) | 4 | 5 | 6 |

The correlation of mean vibration energy dissipation rate

Correlation of mean vibration energy dissipation rate

The correlation of DSE and operational and rock conditions is shown in Figure

Correlation of dynamic specific energy (DSE) and operational parameters for (a) soft rock, (b) moderately hard rock, and (c) hard rock.

The complicated variation of DSE with different advance rate results from the influence of TBM vibration on DSE. The results of DSE in soft rock tunneling for cutterhead rotation speed of 6 rpm and advance rate of 1.2 mm/s are shown in Figure

DSE in soft rock tunneling for

The statistical results, that is, the mean and the standard deviation of percentage increases of maximum DSE and mean DSE relative to SE, are shown in Figure

Percentage increases of maximum DSE and mean of DSE relative to SE.

The change of mean cutter wear rate with the operational and rock conditions is shown in Figure

Correlation of cutter wear rate and operational parameters for (a) soft rock, (b) moderately hard rock, and (c) hard rock.

The time history of wear rate of this cutter is shown in Figure

Cutter wear rate in soft rock tunneling for

The statistical results, that is, the mean and the standard deviation of percentage increases of mean wear rate compared with the wear rate without considering vibration for this cutter, are shown in Figure

Percentage increases of mean cutter wear rate caused by vibration.

The correlation of load sharing coefficient of the cutterhead driving system and operational and rock conditions is shown in Figure

Correlation of load sharing coefficient and operational parameters for (a) soft rock, (b) moderately hard rock, and (c) hard rock.

An on-site measurement of TBM vibration acceleration was performed for the opening hard rock TBM used in an actual water tunnel project. The vibration measurement system consists of a data acquisition system, a laptop, several 3-directional accelerometers, and connecting wires. The time history of acceleration was then acquired during TBM tunneling. The measuring points in this on-site measurement were distributed on main beam and grippers. Figure

Measuring point at (a) main beam back tip and (b) right gripper.

The water tunnel project where the on-site measurement is carried out is in Northeast, China, and is a part of Liaoning Northwest Water Supply Project. The tunneling section at measurement moment is buried at depth of 200 m and is located in a geological fault zone, where the major constituent of rock mass is granodiorite. Rock mass is not very stable in the developed joint fissures zone, with a wide range of rock blocks falling from tunnel arch and water gushing. According to the project office, the rock mass encountered in the measurement section is classified as soft rock or moderately hard rock.

The results of acceleration response at main beam back tip and right gripper obtained by numerical simulation are compared with those obtained from on-site acceleration measurement. For example, Figure

Acceleration responses of (a) simulated time history, (b) simulated spectrum, (c) measured time history, and (d) measured spectrum at main beam back tip in

The correlation of TBM vibration level and operational parameters obtained from this on-site measurement and tunneling data collection is revealed by Figure

Correlation of acceleration RMS in

Correlation of DSE and operational parameters obtained from on-site measurement (dashed red line is the fitted curve of simulation DSE in soft rock tunneling).

From the investigations of TBM performance considering operational and rock conditions, three major concluding remarks can be made as follows.

Structural parameters in this simulation are as follows:

The equivalent damping coefficients can be obtained by using damping ratios as recommended in [

The authors declare no conflicts of interest, including specific financial interests and relationships relevant to subject of this paper.

This work is financially supported by the Basic Research Program of China (973 Program) (Grant no. 2013CB035403).